东海陆架盆地西湖凹陷平湖斜坡带平湖组煤系地层地震沉积学研究

Seismic sedimentological analysis of coal stratigraphy of Pinghu Formation in the Pinghu slope belt, Xihu Sag, East China Sea Shelf Basin

  • 摘要: 西湖凹陷平湖斜坡带油气资源丰富,主要目的层平湖组为一套海陆过渡的含煤地层,埋深大,沉积环境复杂,储层展布认识不清。综合地震、岩芯、测井等资料,深入分析斜坡带平湖组煤系地层发育特征,建立了研究区高精度等时地层格架,在平湖组三级层序内部细分出低位域、海侵域、高位域。在层序格架约束下,创新性地将多数据体迭代分析、多属性综合分析、地震相识别与拼接等技术有效地应用于地震沉积学研究,进行“地震相-沉积相”的有效转化,重建区域沉积体系。研究表明:SQ3低位域内发育早期建设性三角洲和晚期孤立分流河道沉积,水道沿凹陷长轴方向展布;海侵域时期,研究区南部受潮汐影响强,中小规模垂直岸线的潮道频繁发育,向北河控作用增强,发育受潮汐影响的三角洲水下分流河道;高位域发育三角洲平原沉积,以大规模的北西-南东向分流河道沉积为主。

     

    Abstract: The Pinghu Slope belt in the Xihu Sag is rich in oil and gas resources. Pinghu Formation, the main target layer, is a set of coal bearing strata bearing marine-continental transitional facies in large burial depth and complex sedimentary environment. However, the reservoir distribution in it remains unclear. Based on the data of seismic, core, and logging, we deeply analyzed the response characteristics of coal measures of the Pinghu Formation in the slope belt, established the isochronous stratigraphic framework of high-precision coal seams, and recognized lowstand systems tract, transgressive systems tract, and highstand systems tract in the third-order sequence. Under the constraints of sequence framework, technologies such as multi-data iterative analysis, multi-attribute comprehensive analysis, and seismic facies identification and splicing were applied innovatively to the research in seismic sedimentology, to transform from seismic facies to sedimentary facies effectively, and to reconstruct regional sedimentary system. Results show that the SQ3 lowstand system tract reflects constructive deltas in early stage and meandering rivers in later stage, during which channels developed along the long axis of Xihu Sag. The transgressive systems tract manifests small-medium–sized tidal channels perpendicular to shorelines. The highstand systems tract indicates deltaic plain deposits, of which large-scale NW-SE distributary channel deposits are dominated.

     

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